1. Field of the Invention
The present invention relates to a monitoring system in which pieces of information are serially transmitted by time-division-multiplexing from a plurality of monitored units (monitored apparatuses) to a monitoring unit (monitoring apparatus), and relates to an apparatus as a whole implemented with the monitoring unit and the monitored units.
2. Description of the Related Art
There has hitherto been a system in which a monitoring unit monitors statuses of a plurality of monitored units. Recently, it is required to reduce the number of connection signals and to perform efficient information transmission due to an increase in quantity of the information transmitted to the monitoring unit from the plurality of monitored units and an increase in the number of monitored units.
FIG. 1 shows an example of the system in which the monitoring unit executes monitoring of the plurality of monitored units by a polling process of a serial signal. FIG. 1 illustrates a monitoring unit and a plurality of monitored units #1, #2, . . . , #(n-1), #n. The monitoring unit executes polling with respect to each of the plurality of monitored units #1, #2, . . . , #(n-1), #n serially and cyclically, and thus receives pieces of information from the respective monitored units.
In the system shown in FIG. 1, one-polling time is determined, and a quantity of the information transmissible by the monitored unit in this polling time is determined. Further, as the number of the monitored units rises, a polling interval for one monitored unit elongates. Therefore, the monitored unit, if unable to completely transmit the information in one-polling time, must wait for next polling for transmitting the remaining information. Thus, in the polling method using the serial signal, there is a case in which the monitoring unit takes much time for collecting the information from the respective monitored units. Further, in the system illustrated in FIG. 1, it is required that a one-to-one connection between the monitoring unit and each of the monitored units be established via a signal line. Hence, such a problem arises that if the number of the monitored units rises, the number of the connection signal lines increases.
FIG. 2 shows an example in which the information of the respective monitored units is transmitted by use of the time-division-multiplexing serial signal to the monitoring unit (e.g., Patent document 1). In FIG. 2, the plurality of monitored units #1 through #n is connected to the monitoring unit via the signal line in a bus type connection. A fixed-length timeslot is allocated to each of the monitored units #1 through #n, and each of the monitored units #1 through #n transmits the information to the monitoring unit at the timeslot allocated to the monitored unit itself. Namely, pieces of information from the respective monitored units are multiplexed in time-series and thus transmitted to the monitoring unit via the signal line.
In the system illustrated in FIG. 2, the monitoring unit is connected via the signal line to the respective monitored units #1 through #n in the bus type connection, and the information time-division-multiplexed on the signal line from the respective monitored units #1 through #n is transmitted as the serial signals time-division-multiplexed on the signal line to the monitoring unit. In the system shown in FIG. 2, the signal line is shared among the respective monitored units, and hence the problem about the signal line in the system illustrated in FIG. 1 is obviated.
The information multiplexing position (timeslot) allocated to each monitored unit is fixed, and therefore the timeslot can not be changed corresponding to the type and the status of each of the monitored units. Hence, such a problem occurs that the transmission efficiency declines.
Namely, the timeslot length is fixed, whereby a quantity of the information transmissible in one timeslot is determined. Further, the timeslot allocation position is also fixed. Therefore, if the monitored unit transmits the information larger in quantity than the information quantity of one timeslot to the monitoring unit, the information must be transmitted in two or more timeslots. Whereas if the information well smaller in quantity than the information quantity of one timeslot is transmitted, it takes one-timeslot time, and hence there is a case in which the monitoring unit needs to have a considerable period of time for collecting the information from the respective monitored units.
[Patent document 1] Japanese Patent Application Laid-Open Publication No.59-211342 (FIG. 2)